Retain Win32 entry state and trim canvas/platform seams

docs/modernization/roadmap.md

@@ -104,7 +104,9 @@ Current architecture mismatches that must be treated as real blockers:
   while Linux/Web GLFW render-context acquire/present and Linux app-close now
   route through retained local GLFW callback hooks, and retained Apple ObjC
   handles plus storage paths now sit behind one local `platform_legacy`
-  helper instead of being re-read through `App::I` in each touched path.
+  helper instead of being re-read through `App::I` in each touched path, with
+  the retained GLFW window hooks and fallback storage-path return now also
+  using local retained-state helpers instead of direct method-body reads.
 - `src/platform_legacy/legacy_platform_services.*` is still part of the live
   app shell.
 - `pp_panopainter_ui` still depends on `pp_legacy_app`.
@@ -115,7 +117,8 @@ Current architecture mismatches that must be treated as real blockers:
   checkerboard background setup now route through retained draw-merge helpers,
   with the cache-to-screen checkerboard-plane callback setup also reduced and
   the merged-path per-plane merged-texture draw plus the smoothing-mask face
-  shader/draw pass now routed through the same retained helper family.
+  shader/draw pass plus heightmap callback setup now routed through the same
+  retained helper family.
 - `app_layout.cpp` and `app_dialogs.cpp` are still mixed shell/controller files
   rather than thin composition/binding surfaces.
 - `App`, `Canvas`, `Node`, retained workers, and platform entrypoints still use
@@ -128,7 +131,9 @@ Current architecture mismatches that must be treated as real blockers:
   also use owned `std::jthread` lifecycle, `LogRemote` now uses the same
   ownership model, the Windows VR device now has explicit `std::unique_ptr`
   ownership instead of raw global lifetime, and the Windows main-loop/VR
-  coordination flags now use `std::atomic` instead of unsynchronized globals.
+  coordination flags now use `std::atomic` instead of unsynchronized globals,
+  while the main Win32 entrypoint now groups window/GL/task/VR state behind a
+  retained local state object instead of separate process-wide globals.
 - Modern C++23 usage exists in extracted components, especially `std::span`,
   explicit result/status objects, and a few concepts, but the live app still
   does not consistently express ownership, thread affinity, or renderer